Repeaters have long been used in conventional two-way radio systems to extend the coverage range of subscriber units operating in such systems. A repeater operates by receiving communication signals transmitted by a particular subscriber unit on an inbound channel, and by retransmitting the signals at a higher power level on an outbound channel. Subscriber units participating in such radio systems generally have channels programmed to operate in conjunction with a repeater. However, it is common to provide such units with direct unit to unit communication ("talk-around") capability, i.e., the ability to communicate without the aid of a repeater or other infrastructure equipment, in order to support localized or emergency communication when a repeater is not available.
In a typical system, a subscriber unit initiates a call in repeater mode by transmitting a call setup request to the repeater, which request may contain synchronization and control information. Generally, the repeater monitors its inbound channel for an incoming call setup request from an initiating subscriber unit. The repeater responds by executing a call setup procedure that includes transmitting call information received from the initiating subscriber unit on the inbound channel to a corresponding outbound channel. A targeted subscriber unit monitoring the outbound channel receives the transmitted information and the call is completed.
In talk-around mode, the initiating subscriber unit makes a call by transmitting on a channel expected to be monitored by the targeted subscriber unit. Talk-around capability is usually provided on a limited number of channels which are separate from the repeater mode channels. Thus, a user must select one channel or another in order to operate in repeater mode or in talk-around mode. Such user interaction adds complexity to a call setup process because the user must decide whether to initiate a call on a repeater inbound channel or on a talk-around channel, and the target subscriber unit must also be monitoring the correct channel to complete the call.
Oftentimes, a user is interested in maximizing communication range, and would prefer to utilize a repeater when available. Moreover, in an ongoing communication session, when a repeater is no longer available, it would be desirable to switch to talk-around mode if such localized communication is possible. Channel based mode selection, such as used in prior art systems, more laborious than desired. Therefore, a new method for selecting between repeater mode and talk-around mode is needed.